This invention relates generally to a ceramic phosphor manufacturing method, and specifically to a YAG:Ce3+ phosphor made by using aluminum fluoride as a fluxing agent in the garnet synthesis.
White light emitting LEDs are used as a backlight in liquid crystal displays and as a replacement for small conventional and fluorescent lamps. As discussed in chapter 10.4 of xe2x80x9cThe Blue Laser Diodexe2x80x9d by S. Nakamura et al., pages 216-221 Springer 1997), incorporated herein by reference, white light LEDs are fabricated by forming a ceramic phosphor layer on the output surface of a blue emitting semiconductor LED. Conventionally, the blue LED is an InGaN single quantum well LED and the phosphor is a trivalent cerium doped yttrium aluminum garnet (Y3Al5O12:Ce3+ or xe2x80x9cYAG:Ce3+xe2x80x9d). A portion of the blue light emitted by the LED excites the phosphor causing it to emit yellow light. Another portion of the blue light emitted by the LED is transmitted through the phosphor and is mixed with the yellow light emitted by the phosphor. The viewer perceives the mixture of blue and yellow light as a white light.
However, the prior art YAG:Ce3+ phosphor suffers from several disadvantages. First, the quantum efficiency and luminosity of the prior art YAG:Ce3+ phosphor is lower than desired for optimum luminescent characteristics. Second, the prior art YAG:Ce3+ phosphor synthesis process requires maintaining a strong reducing atmosphere or ambient, such as a forming gas (98% N2, 2% H2) atmosphere, during the sintering (i.e., crystallization) step in order to obtain a sufficient crystallization of the phosphor. The requirement for a strong reducing atmosphere during sintering lowers the quantum efficiency of the phosphor, complicates the sintering process and increases the cost of the phosphor.
In accordance with one aspect of the present invention, there is provided a phosphor comprising A3 D5 E12: Ce3+, where A comprises at least one of Y, Gd, Lu, Sm and La; D comprises at least one of Al, Ga, Sc and In; E comprises oxygen and the phosphor luminosity is greater than 435 lumens per watt. Furthermore, E may also comprise fluorine from an AlF3 flux.
In accordance with another aspect of the present invention, there is provided a method of making a phosphor, comprising combining at least one powder comprising yttrium, cerium, aluminum and oxygen with AlF3 to obtain a first mixture, and heating the first mixture to form a solid phosphor body.
In accordance with another aspect of the present invention, there is provided a combination of powders, comprising at least one powder comprising Y, Ce, Al and oxygen in combination with an AlF3 powder.